Mechanisms underlying the loss of mitochondrial membrane potential in glutamate excitotoxicity

Interplay of mitochondrial calcium signalling and reactive oxygen species production in the brain

Intracellular communication and regulation in brain cells is controlled by the ubiquitous Ca2+ and by redox signalling. Both of these independent signalling systems regulate most of the processes in cells including the cell surviving mechanism or cell death. In physiology Ca2+ can regulate and trigger reactive oxygen species (ROS) production by various enzymes and in mitochondria but ROS could also transmit redox signal to calcium levels via modification of calcium channels or phospholipase activity. Changes in calcium or redox signalling could lead to severe pathology resulting in excitotoxicity or oxidative stress. Interaction of the calcium and ROS is essential to trigger opening of mitochondrial permeability transition pore - the initial step of apoptosis, Ca2+ and ROS-induced oxidative stress involved in necrosis and ferroptosis. Here we review the role of redox signalling and Ca2+ in cytosol and mitochondria in the physiology of brain cells - neurons and astrocytes and how this integration can lead to pathology, including ischaemia injury and neurodegeneration.

Spreading depolarization causes reversible neuronal mitochondria fragmentation and swelling in healthy, normally perfused neocortex

Mitochondrial function is tightly linked to morphology, and fragmentation of dendritic mitochondria during noxious conditions suggests loss of function. In the normoxic cortex, spreading depolarization (SD) is a phenomenon underlying migraine aura. It is unknown whether mitochondria structure is affected by normoxic SD. In vivo two-photon imaging followed by quantitative serial section electron microscopy (ssEM) was used to monitor dendritic mitochondria in the normoxic cortex of urethane-anesthetized mature male and female mice during and after SD initiated by focal KCl microinjection. Structural dynamics of dendrites and their mitochondria were visualized by transfecting excitatory, glutamatergic neurons of the somatosensory cortex with bicistronic AAV, which induced tdTomoto labeling in neuronal cytoplasm and mitochondria labeling with roGFP. Normoxic SD triggered rapidly reversible fragmentation of dendritic mitochondria alongside dendritic beading; however, mitochondria took significantly longer to recover. Several rounds of SD resulted in transient mitochondrial fragmentation and dendritic beading without accumulating injury, as both recovered. SsEM corroborated normoxic SD-elicited dendritic and mitochondrial swelling and transformation of the filamentous mitochondrial network into shorter, swollen tubular, and globular structures. Our results revealed normoxic SD-induced disruption of the dendritic mitochondrial structure that might impact mitochondrial bioenergetics during migraine with aura.

Cytisine-N-methylene-(5,7,4'-trihydroxy)- isoflavone ameliorates ischemic stroke-induced brain injury in mouse by regulating the oxidative stress and BDNF-Trkb/Akt pathway

BACKGROUND

A novel compound Cytisine-N-methylene-(5,7,4'-trihydroxy)- isoflavone (LY01) found in the Sophora alopecuroides L is a neuroprotective agent. However, the effect and potential mechanism of LY01 treatment for ischemic stroke (IS) have not been fully elucidated.

AIM OF THE STUDY

The aim of this study is to demonstrate whether LY01 can rescue ischemic stroke-induced brain injury and oxygen-glucose deprivation/reperfusion (OGD/R).

RESULTS

Our results show that intragastric administration of LY01 improves ischemic stroke behaviors in mice, as demonstrated by neurological score, infarct volume, cerebral water content, rotarod test for activity. Compared with the model group, the ginkgo biloba extract (EGb) and LY01 reversed the neurological score, infarct volume, cerebral water content, rotarod test in model mice. Further analysis showed that the LY01 rescued oxidative stress in the model mice, which was reflected in the increased levels of catalase, superoxide dismutase, total antioxidant capacity and decreased levels of malondialdehyde in the serum of the model mice. Moreover, the expression of the brain-derived neurotrophic factor brain-derived neurotrophic factor (BDNF), phosphorylated protein kinase B (p-Akt), Bax, Bcl-2, (p)-tropomysin related kinase B (p-Trkb) was restored and the expression of Bax, glial fibrillary acidic protein (GFAP) in the brains of the model mice was inhibited through LY01 treatment. In the polymerase chain reaction (PCR) data, after giving LY01, the expression in the brains of model mice was that, IL-10 increased and IL-1β, Bax, Bcl-2 decreased. Furthermore, the results indicated that LY01 improved cell viability, reactive oxygen species content, and mitochondrial membrane potential dissipation induced by OGD/R in primary culture of rat cortical neurons. Bax and caspase-3 activity was upregulated compared to the before after treatment with LY01.

CONCLUSIONS

Our study suggests that LY01 reversed ischemic stroke by reducing oxidative stress and activating the BDNF-TrkB/Akt pathway and exerted a neuroprotective action against OGD/R injury via attenuation, a novel approach was suggested to treat ischemic stroke. Our observations justify the traditional use of LY01 for a treatment of IS in nervous system.

Biological regulatory network analysis for targeting the mitochondrial calcium uniporter (MCU) mediated calcium (Ca2+) transport in neurodegenerative disorders

Calcium (Ca2+) has been observed as the most important ion involved in a series of cellular processes and its homeostasis is critical for normal cellular functions. Mitochondrial calcium uniporter (MCU) complex has been recognized as the most important calcium-specific channel located in the inner mitochondrial membrane and is one of the major players in maintaining the Ca2+ homeostasis by transporting Ca2+ across the mitochondrial membrane. Furthermore, dysregulation of the mitochondrial Ca2+ homeostasis has been orchestrated to neurodegenerative response. This necessitates quantitative evaluation of the MCU-dependent mROS production and subsequent cellular responses for more specific therapeutic interventions against neurodegenerative disorders. Towards this goal, here we present a biological regulatory network of MCU to dynamically simulate the MCU-mediated ROS production and its response in neurodegeneration. Previously, ruthenium complex RuRed and its derivatives have been reported to show low nM to high µM potency against MCU to maintain cytosolic Ca2+ (cCa2+) homeostasis by modulating mitochondrial Ca2+ (mCa2+) uptake. Therefore, structural modeling and dynamic simulation of MCU pore-forming subunit is performed to probe the interaction profiling of previously reported Ru265 and its derivatives compounds with MCU. The current study highlighted MCU as a potential drug target in neurodegenerative disorders. Furthermore, ASP261 and GLU264 amino acid residues in DIME motif of MCU pore-forming subunits are identified as crucial for modulating the activity of MCU in neurodegenerative disorders.

Unravelling the complexity of the mitochondrial Ca2+ uniporter: regulation, tissue specificity, and physiological implications

Calcium (Ca2+) signalling acts a pleiotropic message within the cell that is decoded by the mitochondria through a sophisticated ion channel known as the Mitochondrial Ca2+ Uniporter (MCU) complex. Under physiological conditions, mitochondrial Ca2+ signalling is crucial for coordinating cell activation with energy production. Conversely, in pathological scenarios, it can determine the fine balance between cell survival and death. Over the last decade, significant progress has been made in understanding the molecular bases of mitochondrial Ca2+ signalling. This began with the elucidation of the MCU channel components and extended to the elucidation of the mechanisms that regulate its activity. Additionally, increasing evidence suggests molecular mechanisms allowing tissue-specific modulation of the MCU complex, tailoring channel activity to the specific needs of different tissues or cell types. This review aims to explore the latest evidence elucidating the regulation of the MCU complex, the molecular factors controlling the tissue-specific properties of the channel, and the physiological and pathological implications of mitochondrial Ca2+ signalling in different tissues.

Targeting the autophagy-NAD axis protects against cell death in Niemann-Pick type C1 disease models

Impairment of autophagy leads to an accumulation of misfolded proteins and damaged organelles and has been implicated in plethora of human diseases. Loss of autophagy in actively respiring cells has also been shown to trigger metabolic collapse mediated by the depletion of nicotinamide adenine dinucleotide (NAD) pools, resulting in cell death. Here we found that the deficit in the autophagy-NAD axis underpins the loss of viability in cell models of a neurodegenerative lysosomal storage disorder, Niemann-Pick type C1 (NPC1) disease. Defective autophagic flux in NPC1 cells resulted in mitochondrial dysfunction due to impairment of mitophagy, leading to the depletion of both the reduced and oxidised forms of NAD as identified via metabolic profiling. Consequently, exhaustion of the NAD pools triggered mitochondrial depolarisation and apoptotic cell death. Our chemical screening identified two FDA-approved drugs, celecoxib and memantine, as autophagy activators which effectively restored autophagic flux, NAD levels, and cell viability of NPC1 cells. Of biomedical relevance, either pharmacological rescue of the autophagy deficiency or NAD precursor supplementation restored NAD levels and improved the viability of NPC1 patient fibroblasts and induced pluripotent stem cell (iPSC)-derived cortical neurons. Together, our findings identify the autophagy-NAD axis as a mechanism of cell death and a target for therapeutic interventions in NPC1 disease, with a potential relevance to other neurodegenerative disorders.

Energy substrate supplementation increases ATP levels and is protective to PD neurons

Alteration of mitochondrial metabolism by various mutations or toxins leads to various neurological conditions. Age-related changes in energy metabolism could also play the role of a trigger for neurodegenerative disorders. Nonetheless, it is not clear if restoration of ATP production or supplementation of brain cells with substrates for energy production could be neuroprotective. Using primary neurons and astrocytes, and neurons with familial forms of neurodegenerative disorders we studied whether various substrates of energy metabolism could improve mitochondrial metabolism and stimulate ATP production, and whether increased ATP levels could protect cells against glutamate excitotoxicity and neurodegeneration. We found that supplementation of neurons with several substrates, or combination thereof, for the TCA cycle and cellular respiration, and oxidative phosphorylation resulted in an increase in mitochondrial NADH level and in mitochondrial membrane potential and led to an increased level of ATP in neurons and astrocytes. Subsequently, these cells were protected against energy deprivation during ischemia or glutamate excitotoxicity. Provision of substrates for energy metabolism to cells with familial forms of Parkinson's disease also prevented triggering of cell death. Thus, restoration of energy metabolism and increase of ATP production can play neuroprotective role in neurodegeneration. A combination of a succinate salt of choline and nicotinamide provided the best results.

Traumatic Brain Injury: A Comprehensive Review of Biomechanics and Molecular Pathophysiology

Traumatic brain injury (TBI) is a critical public health concern with profound consequences for affected individuals. This comprehensive literature review delves into TBI intricacies, encompassing primary injury biomechanics and the molecular pathophysiology of the secondary injury cascade. Primary TBI involves a complex interplay of forces, including impact loading, blast overpressure, and impulsive loading, leading to diverse injury patterns. These forces can be categorized into inertial (e.g., rotational acceleration causing focal and diffuse injuries) and contact forces (primarily causing focal injuries like skull fractures). Understanding their interactions is crucial for effective injury management. The secondary injury cascade in TBI comprises multifaceted molecular and cellular responses, including altered ion concentrations, dysfunctional neurotransmitter networks, oxidative stress, and cellular energy disturbances. These disruptions impair synaptic function, neurotransmission, and neuroplasticity, resulting in cognitive and behavioral deficits. Moreover, neuroinflammatory responses play a pivotal role in exacerbating damage. As we endeavor to bridge the knowledge gap between biomechanics and molecular pathophysiology, further research is imperative to unravel the nuanced interplay between mechanical forces and their consequences at the molecular and cellular levels, ultimately guiding the development of targeted therapeutic strategies to mitigate the debilitating effects of TBI. In this study, we aim to provide a concise review of the bridge between biomechanical processes causing primary injury and the ensuing molecular pathophysiology of secondary injury, while detailing the subsequent clinical course for this patient population. This knowledge is crucial for advancing our understanding of TBI and developing effective interventions to improve outcomes for those affected.

Neuronal Mitochondrial Calcium Uniporter (MCU) Deficiency Is Neuroprotective in Hyperexcitability by Modulation of Metabolic Pathways and ROS Balance

Epilepsy is one of the most common neurological disorders in the world. Common epileptic drugs generally affect ion channels or neurotransmitters and prevent the emergence of seizures. However, up to a third of the patients suffer from drug-resistant epilepsy, and there is an urgent need to develop new therapeutic strategies that go beyond acute antiepileptic (antiseizure) therapies towards therapeutics that also might have effects on chronic epilepsy comorbidities such as cognitive decline and depression. The mitochondrial calcium uniporter (MCU) mediates rapid mitochondrial Ca2+ transport through the inner mitochondrial membrane. Ca2+ influx is essential for mitochondrial functions, but longer elevations of intracellular Ca2+ levels are closely associated with seizure-induced neuronal damage, which are underlying mechanisms of cognitive decline and depression. Using neuronal-specific MCU knockout mice (MCU-/-ΔN), we demonstrate that neuronal MCU deficiency reduced hippocampal excitability in vivo. Furthermore, in vitro analyses of hippocampal glioneuronal cells reveal no change in total Ca2+ levels but differences in intracellular Ca2+ handling. MCU-/-ΔN reduces ROS production, declines metabolic fluxes, and consequently prevents glioneuronal cell death. This effect was also observed under pathological conditions, such as the low magnesium culture model of seizure-like activity or excitotoxic glutamate stimulation, whereby MCU-/-ΔN reduces ROS levels and suppresses Ca2+ overload seen in WT cells. This study highlights the importance of MCU at the interface of Ca2+ handling and metabolism as a mediator of stress-related mitochondrial dysfunction, which indicates the modulation of MCU as a potential target for future antiepileptogenic therapy.

Spreading depolarization causes reversible neuronal mitochondria fragmentation and swelling in healthy, normally perfused neocortex

Mitochondrial function is tightly linked to their morphology, and fragmentation of dendritic mitochondria during noxious conditions suggests loss of function. In the normoxic cortex, spreading depolarization (SD) is a phenomenon underlying migraine aura. It is unknown whether mitochondria structure is affected by normoxic SD. In vivo two-photon imaging followed by quantitative serial section electron microscopy (ssEM) was used to monitor dendritic mitochondria in the normoxic cortex of urethane-anesthetized mature male and female mice during and after SD initiated by focal KCl microinjection. Structural dynamics of dendrites and their mitochondria were visualized by transfecting excitatory, glutamatergic neurons of the somatosensory cortex with bicistronic AAV, which induced tdTomoto labeling in neuronal cytoplasm and mitochondria labeling with roGFP. Normoxic SD triggered a rapid fragmentation of dendritic mitochondria alongside dendritic beading, both reversible; however, mitochondria took significantly longer to recover. Several rounds of SD resulted in transient mitochondrial fragmentation and dendritic beading without accumulating injury, as both recovered. SsEM corroborated normoxic SD-elicited dendritic and mitochondrial swelling and transformation of the filamentous mitochondrial network into shorter, swollen tubular and globular structures. Our results revealed normoxic SD-induced disruption of the dendritic mitochondrial structure that might impact mitochondrial bioenergetics during migraine with aura.

Neuroprotective Effects of Noncanonical PAR1 Agonists on Cultured Neurons in Excitotoxicity

Serine proteases regulate cell functions through G protein-coupled protease-activated receptors (PARs). Cleavage of one peptide bond of the receptor amino terminus results in the formation of a new N-terminus ("tethered ligand") that can specifically interact with the second extracellular loop of the PAR receptor and activate it. Activation of PAR1 by thrombin (canonical agonist) and activated protein C (APC, noncanonical agonist) was described as a biased agonism. Here, we have supposed that synthetic peptide analogs to the PAR1 tethered ligand liberated by APC could have neuroprotective effects like APC. To verify this hypothesis, a model of the ischemic brain impairment based on glutamate (Glu) excitotoxicity in primary neuronal cultures of neonatal rats has been used. It was shown that the nanopeptide NPNDKYEPF-NH2 (AP9) effectively reduced the neuronal death induced by Glu. The influence of AP9 on cell survival was comparable to that of APC. Both APC and AP9 reduced the dysregulation of intracellular calcium homeostasis in cultured neurons induced by excitotoxic Glu (100 µM) or NMDA (200 µM) concentrations. PAR1 agonist synthetic peptides might be noncanonical PAR1 agonists and a basis for novel neuroprotective drugs for disorders related to Glu excitotoxicity such as brain ischemia, trauma and some neurodegenerative diseases.

Hypertonicity induces mitochondrial extracellular vesicles (MEVs) that activate TNF-α and β-catenin signaling to promote adipocyte dedifferentiation

BACKGROUND

Recent studies demonstrated that elevated osmolarity could induce adipocyte dedifferentiation, representing an appealing procedure to generate multipotent stem cells. Here we aim to elucidate the molecular mechanisms that underlie osmotic induction of adipocyte reprogramming.

METHODS

To induce dedifferentiation, the 3T3-L1 or SVF adipocytes were cultured under the hypertonic pressure in 2% PEG 300 medium. Adipocyte dedifferentiation was monitored by aspect ratio measurement, Oil Red staining and qPCR to examine the morphology, lipid droplets, and specific genes of adipocytes, respectively. The osteogenic and chondrogenic re-differentiation capacities of dedifferentiated adipocytes were also examined. To investigate the mechanisms of the osmotic stress-induced dedifferentiation, extracellular vesicles (EVs) were collected from the reprograming cells, followed by proteomic and functional analyses. In addition, qPCR, ELISA, and TNF-α neutralizing antibody (20 ng/ml) was applied to examine the activation and effects of the TNF-α signaling. Furthermore, we also analyzed the Wnt signaling by assessing the activation of β-catenin and applying BML-284, an agonist of β-catenin.

RESULTS

Hypertonic treatment induced dedifferentiation of both 3T3-L1 and the primary stromal vascular fraction (SVF) adipocytes, characterized by morphological and functional changes. Proteomic profiling revealed that hypertonicity induced extracellular vesicles (EVs) containing mitochondrial molecules including NDUFA9 and VDAC. Functionally, the mitochondrial EVs (MEVs) stimulated TNF-α signaling that activates Wnt-β-catenin signaling and adipocyte dedifferentiation. Neutralizing TNF-α inhibited hypertonic dedifferentiation of adipocytes. In addition, direct activation of Wnt-β-catenin signaling using BML-284 could efficiently induce adipocyte dedifferentiation while circumventing the apoptotic effect of the hypertonic treatment.

CONCLUSIONS

Hypertonicity prompts the adipocytes to release MEVs, which in turn enhances the secretion of TNF-α as a pro-inflammatory cytokine during the stress response. Importantly, TNF-α is essential for the activation of the Wnt/β-catenin signaling that drives adipocyte dedifferentiation. A caveat of the hypertonic treatment is apoptosis, which could be circumvented by direct activation of the Wnt/β-catenin signaling using BML-284.

Ketone body β-hydroxybutyrate (BHB) preserves mitochondrial bioenergetics

The ketogenic diet is an emerging therapeutic approach for refractory epilepsy, as well as certain rare and neurodegenerative disorders. The main ketone body, β-hydroxybutyrate (BHB), is the primary energy substrate endogenously produced in a ketogenic diet, however, mechanisms of its therapeutic actions remain unknown. Here, we studied the effects of BHB on mitochondrial energetics, both in non-stimulated conditions and during glutamate-mediated hyperexcitation. We found that glutamate-induced hyperexcitation stimulated mitochondrial respiration in cultured cortical neurons, and that this response was greater in cultures supplemented with BHB than with glucose. BHB enabled a stronger and more sustained maximal uncoupled respiration, indicating that BHB enables neurons to respond more efficiently to increased energy demands such as induced during hyperexcitation. We found that cytosolic Ca2+ was required for BHB-mediated enhancement of mitochondrial function, and that this enhancement was independent of the mitochondrial glutamate-aspartate carrier, Aralar/AGC1. Our results suggest that BHB exerts its protective effects against hyperexcitation by enhancing mitochondrial function through a Ca2+-dependent, but Aralar/AGC1-independent stimulation of mitochondrial respiration.

A pilot study on glutamate receptor and carrier gene variants and risk of childhood autism spectrum

Imbalanced glutamate signaling has been implicated in the development of autism spectrum disorder (ASD). This case-control study was to examine single nucleotide polymorphisms (SNPs) in glutamate receptor and carrier genes and determine their association with childhood ASD in a Chinese Han population. A total of 12 SNPs in genes encoding glutamate receptors (GRM7 and GRM8) and carriers (SLC1A1 and SLC25A12) were examined in 249 autistic children and 353 healthy controls. The Childhood Autism Rating Scale (CARS) and its verbal communication domain were applied to evaluate the severity of the disease and language impairment, respectively. The T allele of rs2292813 in the SLC25A12 gene was significantly associated with an increased risk of ASD (odds ratio (OD) = 1.7, 95% confidence interval (CI): 1.1-2.6, P = 0.0107). Neither the genotypes nor allele distributions of other SNPs were associated with the risk of ASD. Notably, rs1800656 and rs2237731 in the GRM8 gene, but not other SNPs, were related to the severity of language impairment. All SNPs were not correlated with the overall severity of ASD. Our findings support associations between the SLC25A12 gene variant and the risk of childhood ASD, and between the GRM8 gene variant and the severity of language impairment in the Chinese Han population.

Beneficial Effects of Halogenated Anesthetics in Cardiomyocytes: The Role of Mitochondria

In the last few years, the use of anesthetic drugs has been related to effects other than those initially related to their fundamental effect, hypnosis. Halogenated anesthetics, mainly sevoflurane, have been used as a therapeutic tool in patients undergoing cardiac surgery, thanks to the beneficial effect of the cardiac protection they generate. This effect has been described in several research studies. The mechanism by which they produce this effect has been associated with the effects generated by anesthetic preconditioning and postconditioning. The mechanisms by which these effects are induced are directly related to the modulation of oxidative stress and the cellular damage generated by the ischemia/reperfusion procedure through the overexpression of different enzymes, most of them included in the Reperfusion Injury Salvage Kinase (RISK) and the Survivor Activating Factor Enhancement (SAFE) pathways. Mitochondria is the final target of the different routes of pre- and post-anesthetic conditioning, and it is preserved from the damage generated in moments of lack of oxygen and after the recovery of the normal oxygen concentration. The final consequence of this effect has been related to better cardiac function in this type of patient, with less myocardial damage, less need for inotropic drugs to achieve normal myocardial function, and a shorter hospital stay in intensive care units. The mechanisms through which mitochondrial homeostasis is maintained and its relationship with the clinical effect are the basis of our review. From a translational perspective, we provide information regarding mitochondrial physiology and physiopathology in cardiac failure and the role of halogenated anesthetics in modulating oxidative stress and inducing myocardial conditioning.

Sex-dependent neuronal effects of α-synuclein reveal that GABAergic transmission is neuroprotective of sleep-controlling neurons

BACKGROUND

Sleep disorders (SDs) are a symptom of the prodromal phase of neurodegenerative disorders that are mechanistically linked to the protein α-synuclein (α-syn) including Parkinson's disease (PD). SDs during the prodromal phase could result from neurodegeneration induced in state-controlling neurons by accumulation of α-syn predominant early in the disease, and consistent with this, we reported the monomeric form of α-syn (monomeric α-syn; α-synM) caused cell death in the laterodorsal tegmental nucleus (LDT), which controls arousal as well as the sleep and wakefulness state. However, we only examined the male LDT, and since sex is considered a risk factor for the development of α-syn-related diseases including prodromal SDs, the possibility exists of sex-based differences in α-synM effects. Accordingly, we examined the hypothesis that α-synM exerts differential effects on membrane excitability, intracellular calcium, and cell viability in the LDT of females compared to males.

METHODS

Patch clamp electrophysiology, bulk load calcium imaging, and cell death histochemistry were used in LDT brain slices to monitor responses to α-synM and effects of GABA receptor acting agents.

RESULTS

Consistent with our hypothesis, we found differing effects of α-synM on female LDT neurons when compared to male. In females, α-synM induced a decrease in membrane excitability and heightened reductions in intracellular calcium, which were reliant on functional inhibitory acid transmission, as well as decreased the amplitude and frequency of spontaneous excitatory postsynaptic currents (sEPSCs) with a concurrent reduction in action potential firing rate. Cell viability studies showed higher α-synM-mediated neurodegeneration in males compared to females that depended on inhibitory amino acid transmission. Further, presence of GABA receptor agonists was associated with reduced cell death in males.

CONCLUSIONS

When taken together, we conclude that α-synM induces a sex-dependent effect on LDT neurons involving a GABA receptor-mediated mechanism that is neuroprotective. Understanding the potential sex differences in neurodegenerative processes, especially those occurring early in the disease, could enable implementation of sex-based strategies to identify prodromal PD cases, and promote efforts to illuminate new directions for tailored treatment and management of PD.

NLRP3 inflammasome activation after ischemic stroke

Cerebral ischemia is a pathological condition resulting from the cessation or reduction of blood supply to the cerebral arteries. Neurological deficits that are clinically relevant can arise as a result of brain damage. The etiology of stroke is multifaceted and intricate, with the inflammatory response being a crucial component that warrants significant attention. Following a cerebrovascular accident, the levels of interleukin-1 beta and interleukin-18 within the central nervous system escalate due to the activation of the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 inflammasome. The inflammation is aggravated by the subsequent occurrence of pyroptosis. The mechanisms that activate the NLRP3 inflammasome pyroptosis signaling pathway axis are described in this article. In addition, we go over how pyroptosis interacts with other processes for regulated cell death. In addition, specific NLRP3 inflammasome pathway inhibitors are identified, which offer new approaches to preventing ischemic brain injury.

Extrasynaptic NMDA receptors in acute and chronic excitotoxicity: implications for preventive treatments of ischemic stroke and late-onset Alzheimer's disease

Stroke and late-onset Alzheimer's disease (AD) are risk factors for each other; the comorbidity of these brain disorders in aging individuals represents a significant challenge in basic research and clinical practice. The similarities and differences between stroke and AD in terms of pathogenesis and pathophysiology, however, have rarely been comparably reviewed. Here, we discuss the research background and recent progresses that are important and informative for the comorbidity of stroke and late-onset AD and related dementia (ADRD). Glutamatergic NMDA receptor (NMDAR) activity and NMDAR-mediated Ca²⁺ influx are essential for neuronal function and cell survival. An ischemic insult, however, can cause rapid increases in glutamate concentration and excessive activation of NMDARs, leading to swift Ca²⁺ overload in neuronal cells and acute excitotoxicity within hours and days. On the other hand, mild upregulation of NMDAR activity, commonly seen in AD animal models and patients, is not immediately cytotoxic. Sustained NMDAR hyperactivity and Ca²⁺ dysregulation lasting from months to years, nevertheless, can be pathogenic for slowly evolving events, i.e. degenerative excitotoxicity, in the development of AD/ADRD. Specifically, Ca²⁺ influx mediated by extrasynaptic NMDARs (eNMDARs) and a downstream pathway mediated by transient receptor potential cation channel subfamily M member (TRPM) are primarily responsible for excitotoxicity. On the other hand, the NMDAR subunit GluN3A plays a "gatekeeper" role in NMDAR activity and a neuroprotective role against both acute and chronic excitotoxicity. Thus, ischemic stroke and AD share an NMDAR- and Ca²⁺-mediated pathogenic mechanism that provides a common receptor target for preventive and possibly disease-modifying therapies. Memantine (MEM) preferentially blocks eNMDARs and was approved by the Federal Drug Administration (FDA) for symptomatic treatment of moderate-to-severe AD with variable efficacy. According to the pathogenic role of eNMDARs, it is conceivable that MEM and other eNMDAR antagonists should be administered much earlier, preferably during the presymptomatic phases of AD/ADRD. This anti-AD treatment could simultaneously serve as a preconditioning strategy against stroke that attacks ≥ 50% of AD patients. Future research on the regulation of NMDARs, enduring control of eNMDARs, Ca²⁺ homeostasis, and downstream events will provide a promising opportunity to understand and treat the comorbidity of AD/ADRD and stroke.

Structure-Activity Relationships of Metal-Based Inhibitors of the Mitochondrial Calcium Uniporter

The mitochondrial calcium uniporter (MCU) is a transmembrane protein that is responsible for mediating mitochondrial calcium (mCa2+ ) uptake. Given this critical function, the MCU has been implicated as an important target for addressing various human diseases. As such, there has a been growing interest in developing small molecules that can inhibit this protein. To date, metal coordination complexes, particularly multinuclear ruthenium complexes, are the most widely investigated MCU inhibitors due to both their potent inhibitory activities as well as their longstanding use for this application. Recent efforts have expanded the metal-based toolkit for MCU inhibition. This concept paper summarizes the development of new metal-based inhibitors of the MCU and their structure-activity relationships in the context of improving their potential for therapeutic use in managing human diseases related to mCa2+ dysregulation.

Plasticity of perisynaptic astroglia during ischemia-induced spreading depolarization

High astroglial capacity for glutamate and potassium clearance aids in recovering spreading depolarization (SD)-evoked disturbance of ion homeostasis during stroke. Since perisynaptic astroglia cannot be imaged with diffraction-limited light microscopy, nothing is known about the impact of SD on the ultrastructure of a tripartite synapse. We used serial section electron microscopy to assess astroglial synaptic coverage in the sensorimotor cortex of urethane-anesthetized male and female mice during and after SD evoked by transient bilateral common carotid artery occlusion. At the subcellular level, astroglial mitochondria were remarkably resilient to SD compared to dendritic mitochondria that were fragmented by SD. Overall, 482 synapses in `Sham' during `SD' and `Recovery' groups were randomly selected and analyzed in 3D. Perisynaptic astroglia was present at the axon-spine interface (ASI) during SD and after recovery. Astrocytic processes were more likely found at large synapses on mushroom spines after recovery, while the length of the ASI perimeter surrounded by astroglia has also significantly increased at large synapses. These findings suggest that as larger synapses have a bigger capacity for neurotransmitter release during SD, they attract astroglial processes to their perimeter during recovery, limiting extrasynaptic glutamate escape and further enhancing the astrocytic ability to protect synapses in stroke.

Dinuclear nitrido-bridged osmium complexes inhibit the mitochondrial calcium uniporter and protect cortical neurons against lethal oxygen-glucose deprivation

Dysregulation of mitochondrial calcium uptake mediated by the mitochondrial calcium uniporter (MCU) is implicated in several pathophysiological conditions. Dinuclear ruthenium complexes are effective inhibitors of the MCU and have been leveraged as both tools to study mitochondrial calcium dynamics and potential therapeutic agents. In this study, we report the synthesis and characterization of Os245 ([Os2(μ-N)(NH3)8Cl2]3+) which is the osmium-containing analogue of our previously reported ruthenium-based inhibitor Ru265. This complex and its aqua-capped analogue Os245' ([Os2(μ-N)(NH3)8(OH2)2]5+) are both effective inhibitors of the MCU in permeabilized and intact cells. In comparison to the ruthenium-based inhibitor Ru265 (k obs = 4.92 × 10-3 s-1), the axial ligand exchange kinetics of Os245 are two orders of magnitude slower (k obs = 1.63 × 10-5 s-1) at 37 °C. The MCU-inhibitory properties of Os245 and Os245' are different (Os245 IC50 for MCU inhibition = 103 nM; Os245' IC50 for MCU inhibition = 2.3 nM), indicating that the axial ligands play an important role in their interactions with this channel. We further show that inhibition of the MCU by these complexes protects primary cortical neurons against lethal oxygen-glucose deprivation. When administered in vivo to mice (10 mg kg-1), Os245 and Os245' induce seizure-like behaviors in a manner similar to the ruthenium-based inhibitors. However, the onset of these seizures is delayed, a possible consequence of the slower ligand substitution kinetics for these osmium complexes. These findings support previous studies that demonstrate inhibition of the MCU is a promising therapeutic strategy for the treatment of ischemic stroke, but also highlight the need for improved drug delivery strategies to mitigate the pro-convulsant effects of this class of complexes before they can be implemented as therapeutic agents. Furthermore, the slower ligand substitution kinetics of the osmium analogues may afford new strategies for the development and modification of this class of MCU inhibitors.

MAPT genotype-dependent mitochondrial aberration and ROS production trigger dysfunction and death in cortical neurons of patients with hereditary FTLD

Tauopathies are a major type of proteinopathies underlying neurodegenerative diseases. Mutations in the tau-encoding MAPT-gene lead to hereditary cases of frontotemporal lobar degeneration (FTLD)-tau, which span a wide phenotypic and pathological spectrum. Some of these mutations, such as the N279K mutation, result in a shift of the physiological 3R/4R ratio towards the more aggregation prone 4R isoform. Other mutations such as V337M cause a decrease in the in vitro affinity of tau to microtubules and a reduced ability to promote microtubule assembly. Whether both mutations address similar downstream signalling cascades remains unclear but is important for potential rescue strategies. Here, we developed a novel and optimised forward programming protocol for the rapid and highly efficient production of pure cultures of glutamatergic cortical neurons from hiPSCs. We apply this protocol to delineate mechanisms of neurodegeneration in an FTLD-tau hiPSC-model consisting of MAPT^N279K- or MAPT^V337M-mutants and wild-type or isogenic controls. The resulting cortical neurons express MAPT-genotype-dependent dominant proteome clusters regulating apoptosis, ROS homeostasis and mitochondrial function. Related pathways are significantly upregulated in MAPT^N279K neurons but not in MAPT^V337M neurons or controls. Live cell imaging demonstrates that both MAPT mutations affect excitability of membranes as reflected in spontaneous and stimulus evoked calcium signals when compared to controls, albeit more pronounced in MAPT^N279K neurons. These spontaneous calcium oscillations in MAPT^N279K neurons triggered mitochondrial hyperpolarisation and fission leading to mitochondrial ROS production, but also ROS production through NOX2 acting together to induce cell death. Importantly, we found that these mechanisms are MAPT mutation-specific and were observed in MAPT^N279K neurons, but not in MAPT^V337M neurons, supporting a pathological role of the 4R tau isoform in redox disbalance and highlighting MAPT-mutation specific clinicopathological-genetic correlations, which may inform rescue strategies in different MAPT mutations.

Autophagy promotes cell survival by maintaining NAD levels

Autophagy is an essential catabolic process that promotes the clearance of surplus or damaged intracellular components. Loss of autophagy in age-related human pathologies contributes to tissue degeneration through a poorly understood mechanism. Here, we identify an evolutionarily conserved role of autophagy from yeast to humans in the preservation of nicotinamide adenine dinucleotide (NAD) levels, which are critical for cell survival. In respiring mouse fibroblasts with autophagy deficiency, loss of mitochondrial quality control was found to trigger hyperactivation of stress responses mediated by NADases of PARP and Sirtuin families. Uncontrolled depletion of the NAD(H) pool by these enzymes ultimately contributed to mitochondrial membrane depolarization and cell death. Pharmacological and genetic interventions targeting several key elements of this cascade improved the survival of autophagy-deficient yeast, mouse fibroblasts, and human neurons. Our study provides a mechanistic link between autophagy and NAD metabolism and identifies targets for interventions in human diseases associated with autophagic, lysosomal, and mitochondrial dysfunction.

Mitochondria regulate TRPV4-mediated release of ATP

BACKGROUND AND PURPOSE

Ca2+ influx via TRPV4 channels triggers Ca2+ release from the IP3 -sensitive internal store to generate repetitive oscillations. Although mitochondria are acknowledged regulators of IP3 -mediated Ca2+ release, how TRPV4-mediated Ca2+ signals are regulated by mitochondria is unknown. We show that depolarised mitochondria switch TRPV4 signalling from relying on Ca2+ -induced Ca2+ release at IP3 receptors to being independent of Ca2+ influx and instead mediated by ATP release via pannexins.

EXPERIMENTAL APPROACH

TRPV4-evoked Ca2+ signals were individually examined in hundreds of cells in the endothelium of rat mesenteric resistance arteries using the indicator Cal520.

KEY RESULTS

TRPV4 activation with GSK1016790A (GSK) generated repetitive Ca2+ oscillations that required Ca2+ influx. However, when the mitochondrial membrane potential was depolarised, by the uncoupler CCCP or complex I inhibitor rotenone, TRPV4 activation generated large propagating, multicellular, Ca2+ waves in the absence of external Ca2+ . The ATP synthase inhibitor oligomycin did not potentiate TRPV4-mediated Ca2+ signals. GSK-evoked Ca2+ waves, when mitochondria were depolarised, were blocked by the TRPV4 channel blocker HC067047, the SERCA inhibitor cyclopiazonic acid, the PLC blocker U73122 and the inositol trisphosphate receptor blocker caffeine. The Ca2+ waves were also inhibited by the extracellular ATP blockers suramin and apyrase and the pannexin blocker probenecid.

CONCLUSION AND IMPLICATIONS

These results highlight a previously unknown role of mitochondria in shaping TRPV4-mediated Ca2+ signalling by facilitating ATP release. When mitochondria are depolarised, TRPV4-mediated release of ATP via pannexin channels activates plasma membrane purinergic receptors to trigger IP3 -evoked Ca2+ release.

Interaction of Mitochondrial Calcium and ROS in Neurodegeneration

Neurodegenerative disorders are currently incurable devastating diseases which are characterized by the slow and progressive loss of neurons in specific brain regions. Progress in the investigation of the mechanisms of these disorders helped to identify a number of genes associated with familial forms of these diseases and a number of toxins and risk factors which trigger sporadic and toxic forms of these diseases. Recently, some similarities in the mechanisms of neurodegenerative diseases were identified, including the involvement of mitochondria, oxidative stress, and the abnormality of Ca2+ signaling in neurons and astrocytes. Thus, mitochondria produce reactive oxygen species during metabolism which play a further role in redox signaling, but this may also act as an additional trigger for abnormal mitochondrial calcium handling, resulting in mitochondrial calcium overload. Combinations of these factors can be the trigger of neuronal cell death in some pathologies. Here, we review the latest literature on the crosstalk of reactive oxygen species and Ca2+ in brain mitochondria in physiology and beyond, considering how changes in mitochondrial metabolism or redox signaling can convert this interaction into a pathological event.

Excitotoxicity, calcium and mitochondria: a triad in synaptic neurodegeneration

Glutamate is the most commonly engaged neurotransmitter in the mammalian central nervous system, acting to mediate excitatory neurotransmission. However, high levels of glutamatergic input elicit excitotoxicity, contributing to neuronal cell death following acute brain injuries such as stroke and trauma. While excitotoxic cell death has also been implicated in some neurodegenerative disease models, the role of acute apoptotic cell death remains controversial in the setting of chronic neurodegeneration. Nevertheless, it is clear that excitatory synaptic dysregulation contributes to neurodegeneration, as evidenced by protective effects of partial N-methyl-D-aspartate receptor antagonists. Here, we review evidence for sublethal excitatory injuries in relation to neurodegeneration associated with Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis and Huntington's disease. In contrast to classic excitotoxicity, emerging evidence implicates dysregulation of mitochondrial calcium handling in excitatory post-synaptic neurodegeneration. We discuss mechanisms that regulate mitochondrial calcium uptake and release, the impact of LRRK2, PINK1, Parkin, beta-amyloid and glucocerebrosidase on mitochondrial calcium transporters, and the role of autophagic mitochondrial loss in axodendritic shrinkage. Finally, we discuss strategies for normalizing the flux of calcium into and out of the mitochondrial matrix, thereby preventing mitochondrial calcium toxicity and excitotoxic dendritic loss. While the mechanisms that underlie increased uptake or decreased release of mitochondrial calcium vary in different model systems, a common set of strategies to normalize mitochondrial calcium flux can prevent excitatory mitochondrial toxicity and may be neuroprotective in multiple disease contexts.

Olfactory Bulb Excitotoxicity as a Gap-Filling Mechanism Underlying the Link Between Traumatic Brain Injury-Induced Secondary Neuronal Degeneration and Parkinson's Disease-Like Pathology

There is increasing preclinical and clinical data supporting a potential association between Traumatic Brain Injury (TBI) and Parkinson's disease (PD). It has been suggested that the glutamate-induced excitotoxicity underlying TBI secondary neuronal degeneration (SND) might be associated with further development of PD. Interestingly, an accumulation of extracellular glutamate and olfactory dysfunction are both sharing pathological conditions in TBI and PD. The possible involvement of glutamate excitotoxicity in olfactory dysfunction has been recently described, however, the role of olfactory bulbs (OB) glutamate excitotoxicity as a possible mechanism involved in the association between TBI and PD-related neurodegeneration has not been investigated yet. We examined the number of nigral dopaminergic neurons (TH +), nigral α-synuclein expression, the striatal dopamine transporter (DAT) expression, and motor performance after bilateral OB N-Methyl-D-Aspartate (NMDA)-induced excitotoxic lesions in rodents. Bulbar NMDA administration induced a decrease in the number of correct choices in the discrimination tests one week after lesions (p < 0.01) and a significant decrease in the number of nigral DAergic neurons (p < 0.01) associated with an increase in α-synuclein expression (p < 0.01). No significant striatal changes in DAT expression or motor alterations were observed. Our results show an association between TBI-induced SND and PD-related neurodegeneration suggesting that the OB excitotoxicity occurring in TBI SND may be a filling gap mechanism underlying the link between TBI and PD-like pathology.

Lipopolysaccharide From E. coli Increases Glutamate-Induced Disturbances of Calcium Homeostasis, the Functional State of Mitochondria, and the Death of Cultured Cortical Neurons

Lipopolysaccharide (LPS), a fragment of the bacterial cell wall, specifically interacting with protein complexes on the cell surface, can induce the production of pro-inflammatory and apoptotic signaling molecules, leading to the damage and death of brain cells. Similar effects have been noted in stroke and traumatic brain injury, when the leading factor of death is glutamate (Glu) excitotoxicity too. But being an amphiphilic molecule with a significant hydrophobic moiety and a large hydrophilic region, LPS can also non-specifically bind to the plasma membrane, altering its properties. In the present work, we studied the effect of LPS from Escherichia coli alone and in combination with the hyperstimulation of Glu-receptors on the functional state of mitochondria and Ca2+ homeostasis, oxygen consumption and the cell survival in primary cultures from the rats brain cerebellum and cortex. In both types of cultures, LPS (0.1–10 μg/ml) did not change the intracellular free Ca2+ concentration ([Ca2+]i) in resting neurons but slowed down the median of the decrease in [Ca2+]i on 14% and recovery of the mitochondrial potential (ΔΨm) after Glu removal. LPS did not affect the basal oxygen consumption rate (OCR) of cortical neurons; however, it did decrease the acute OCR during Glu and LPS coapplication. Evaluation of the cell culture survival using vital dyes and the MTT assay showed that LPS (10 μg/ml) and Glu (33 μM) reduced jointly and separately the proportion of live cortical neurons, but there was no synergism or additive action. LPS-effects was dependent on the type of culture, that may be related to both the properties of neurons and the different ratio between neurons and glial cells in cultures. The rapid manifestation of these effects may be the consequence of the direct effect of LPS on the rheological properties of the cell membrane.

Neuroprotective effects of an in vitro BBB permeable phenoxythiophene sulfonamide small molecule in glutamate-induced oxidative injury

Reactive oxygen species (ROS) play a central role in oxidative stress-associated neuronal cell death during ischemia. Further investigation into the inhibition of excessive ROS generation post-stroke is urgently required for the treatment of ischemic stroke. In the present study, the neuroprotective properties of the blood-brain barrier (BBB) penetrant B355227 were investigated. B355227 is a chemical analogue of B355252, and the role of the phenoxythiophene sulfonamide compound B355227 was further investigated in a glutamate-induced oxidative injury model. An in vitro model of the BBB was established in the immortalized mouse brain capillary endothelial cell line, bEnd.3. Formation of barrier in Transwell inserts was confirmed using EVOM resistance meter and Caffeine, Imatinib and Axitinib were used to validate the efficacy of the model. The validated BBB assay in combination with high performance liquid chromatography were used to analyse and verify the permeability of B355227 through the barrier. The integrity of the cell junctions after the BBB assays were confirmed using immunofluorescence to visualize the expression of the barrier junction protein zonula occludens-1. Cell survival was measured with Resazurin, a redox indicator dye, in HT22, a hippocampal neuronal cell treated with 5 mM glutamate or co-treated with the B355227 recovered from the BBB permeability experiment. Changes in glutathione levels were detected using a glutathione detection kit, while analyses of ROS, calcium (Ca2+), and mitochondrial membrane potential (MMP) were accomplished with the fluorescent dyes 2',7'-dichlorofluorescein diacetate, Fura-2 AM and MitoTracker Red dyes, respectively. Immunoblotting was also performed to detect the expression and activation of Erk1/2, p-38, JNK, Bax and Bcl-2. The results of the present study demonstrated that B355227 crossed the BBB in vitro and protected HT22 from oxidative injury induced by glutamate exposure. Treatment of cells with B355227 blocked the glutamate-dependent depletion of intracellular glutathione and significantly reduced ROS production. Increased Ca2+ influx and subsequent collapse of the MMP was attenuated by B355227. Furthermore, the results of the present study demonstrated that B355227 protected against oxidative stress via the MAPK pathway, by increasing the activation of Erk1/2, JNK and P38, and restoring anti-apoptotic Bcl-2. Collectively, the results of the present study indicate that B355227 has potent antioxidant and neuroprotective attributes in glutamate-induced neuronal cell death. Further investigation into the role of B355227 in the modulation of glutamate-dependent oxidative stress is required.

Disrupted expression of mitochondrial NCLX sensitizes neuroglial networks to excitotoxic stimuli and renders synaptic activity toxic

The mitochondrial sodium/calcium/lithium exchanger (NCLX) is an important mediator of calcium extrusion from mitochondria. In this study, we tested the hypothesis that physiological expression levels of NCLX are essential for maintaining neuronal resilience in the face of excitotoxic challenge. Using a short hairpin RNA (shRNA)-mediated approach, we showed that reduced NCLX expression exacerbates neuronal mitochondrial calcium dysregulation, mitochondrial membrane potential (ΔΨ_m) breakdown, and reactive oxygen species (ROS) generation during excitotoxic stimulation of primary hippocampal cultures. Moreover, NCLX knockdown-which affected both neurons and glia-resulted not only in enhanced neurodegeneration following an excitotoxic insult, but also in neuronal and astrocytic cell death under basal conditions. Our data also revealed that synaptic activity, which promotes neuroprotective signaling, can become lethal upon NCLX depletion; expression of NCLX-targeted shRNA impaired the clearance of mitochondrial calcium following action potential bursts and was associated both with ΔΨ_mbreakdown and substantial neurodegeneration in hippocampal cultures undergoing synaptic activity. Finally, we showed that NCLX knockdown within the hippocampal cornu ammonis 1 (CA1) region in vivo causes substantial neuro- and astrodegeneration. In summary, we demonstrated that dysregulated NCLX expression not only sensitizes neuroglial networks to excitotoxic stimuli but notably also renders otherwise neuroprotective synaptic activity toxic. These findings may explain the emergence of neuro- and astrodegeneration in patients with disorders characterized by disrupted NCLX expression or function, and suggest that treatments aimed at enhancing or restoring NCLX function may prevent central nervous system damage in these disease states.

The Nanotheranostic Researcher’s Guide for Use of Animal Models of Traumatic Brain Injury

Traumatic brain injury (TBI) is currently the leading cause of injury-related morbidity and mortality worldwide, with an estimated global cost of USD 400 billion annually. Both clinical and preclinical behavioral outcomes associated with TBI are heterogeneous in nature and influenced by the mechanism and frequency of injury. Previous literature has investigated this relationship through the development of animal models and behavioral tasks. However, recent advancements in these methods may provide insight into the translation of therapeutics into a clinical setting. In this review, we characterize various animal models and behavioral tasks to provide guidelines for evaluating the therapeutic efficacy of treatment options in TBI. We provide a brief review into the systems utilized in TBI classification and provide comparisons to the animal models that have been developed. In addition, we discuss the role of behavioral tasks in evaluating outcomes associated with TBI. Our goal is to provide those in the nanotheranostic field a guide for selecting an adequate TBI animal model and behavioral task for assessment of outcomes to increase research in this field.

Understanding the Connection Between Common Stroke Comorbidities, Their Associated Inflammation, and the Course of the Cerebral Ischemia/Reperfusion Cascade

Despite the enormous progress in the understanding of the course of the ischemic stroke over the last few decades, a therapy that effectively protects neurovascular units (NVUs) and significantly improves neurological functions in stroke patients has still not been achieved. The reasons for this state are unclear, but it is obvious that the cerebral ischemia and reperfusion cascade is a highly complex phenomenon, which includes the intense neuroinflammatory processes, and comorbid stroke risk factors strongly worsen stroke outcomes and likely make a substantial contribution to the pathophysiology of the ischemia/reperfusion, enhancing difficulties in searching of successful treatment. Common concomitant stroke risk factors (arterial hypertension, diabetes mellitus and hyperlipidemia) strongly drive inflammatory processes during cerebral ischemia/reperfusion; because these factors are often present for a long time before a stroke, causing low-grade background inflammation in the brain, and already initially disrupting the proper functions of NVUs. Broad consideration of this situation in basic research may prove to be crucial for the success of future clinical trials of neuroprotection, vasculoprotection and immunomodulation in stroke. This review focuses on the mechanism by which coexisting common risk factors for stroke intertwine in cerebral ischemic/reperfusion cascade and the dysfunction and disintegration of NVUs through inflammatory processes, principally activation of pattern recognition receptors, alterations in the expression of adhesion molecules and the subsequent pathophysiological consequences.

Neuroprotective Effects of Exogenous Irisin in Kainic Acid-Induced Status Epilepticus

Elevated reactive oxygen species (ROS) level is considered a crucial causative factor for neuronal damage in epilepsy. Irisin has been reported to ameliorate mitochondrial dysfunction and to reduce ROS levels; therefore, in this study, the effect of exogenous irisin on neuronal injury was evaluated in rats with kainic acid (KA)-induced status epilepticus (SE). Our results showed that exogenous irisin treatment significantly increased the expression of brain-derived neurotrophic factor (BDNF) and uncoupling protein 2 (UCP2), and reduced the levels of neuronal injury and mitochondrial oxidative stress. Additionally, an inhibitor of UCP2 (genipin) was administered to investigate the underlying mechanism of irisin-induced neuroprotection; in rats treated with genipin, the neuroprotective effects of irisin on KA-induced SE were found to be partially reversed. Our findings confirmed the neuroprotective effects of exogenous irisin and provide evidence that these effects may be mediated via the BDNF/UCP2 pathway, thus providing valuable insights that may aid the development of exogenous irisin treatment as a potential therapeutic strategy against neuronal injury in epilepsy.

Protective role of taurine against oxidative stress (Review)

Taurine is a fundamental mediator of homeostasis that exerts multiple roles to confer protection against oxidant stress. The development of hypertension, muscle/neuro‑​associated disorders, hepatic cirrhosis, cardiac dysfunction and ischemia/reperfusion are examples of some injuries that are linked with oxidative stress. The present review gives a comprehensive description of all the underlying mechanisms of taurine, with the aim to explain its anti‑oxidant actions. Taurine is regarded as a cytoprotective molecule due to its ability to sustain normal electron transport chain, maintain glutathione stores, upregulate anti‑oxidant responses, increase membrane stability, eliminate inflammation and prevent calcium accumulation. In parallel, the synergistic effect of taurine with other potential therapeutic modalities in multiple disorders are highlighted. Apart from the results derived from research findings, the current review bridges the gap between bench and bedside, providing mechanistic insights into the biological activity of taurine that supports its potential therapeutic efficacy in clinic. In the future, further clinical studies are required to support the ameliorative effect of taurine against oxidative stress.

17-β Estradiol Rescued Immature Rat Brain against Glutamate-Induced Oxidative Stress and Neurodegeneration via Regulating Nrf2/HO-1 and MAP-Kinase Signaling Pathway

Dysregulated glutamate signaling, leading to neuronal excitotoxicity and death, has been associated with neurodegenerative pathologies. 17β-estradiol (E2) is a human steroid hormone having a role in reproduction, sexual maturation, brain health and biological activities. The study aimed to explain the neuroprotective role of E2 against glutamate-induced ROS production, MAP kinase-dependent neuroinflammation, synaptic dysfunction and neurodegeneration in the cortex and hippocampus of postnatal day 7 rat brain. Biochemical and immunofluorescence analyses were applied. Our results showed that a single subcutaneous injection of glutamate (10 mg/kg) induced brain oxidative stress after 4 h by disturbing the homeostasis of glutathione (GSH) and revealed an upsurge in ROS and LPO levels and downregulated the expression of Nrf2 and HO-1 antioxidant protein. The glutamate-exposed P7 pups illustrated increased phosphorylation of stress-activated c-Jun N-terminal kinase (JNK) and p38 kinase (p38) and downregulated expression of P-Erk1/2. This was accompanied by pathological neuroinflammation as revealed by enhanced gliosis with upregulated expression of GFAP and Iba-1, and the activation of proinflammatory cytokines (TNF-α) in glutamate-injected P7 pups. Moreover, exogenous glutamate also reduced the expression of synaptic markers (PSD-95, SYP) and induced apoptotic neurodegeneration in the cortical and hippocampal regions by dysregulating the expression of Bax, Bcl-2 and caspase-3 in the developing rat brain. On the contrary, co-treatment of E2 (10 mg/kg) with glutamate significantly abrogated brain neuroinflammation, neurodegeneration and synapse loss by alleviating brain oxidative stress by upregulating the Nrf2/HO-1 antioxidant pathway and by deactivating pro-apoptotic P-JNK/P-p38 and activation of pro-survival P-Erk1/2 MAP kinase pathways. In brief, the data demonstrate the neuroprotective role of E2 against glutamate excitotoxicity-induced neurodegeneration. The study also encourages future studies investigating if E2 may be a potent neuroprotective and neurotherapeutic agent in different neurodegenerative diseases.

Mitochondrial ROS control neuronal excitability and cell fate in frontotemporal dementia

INTRODUCTION

The second most common form of early-onset dementia-frontotemporal dementia (FTD)-is often characterized by the aggregation of the microtubule-associated protein tau. Here we studied the mechanism of tau-induced neuronal dysfunction in neurons with the FTD-related 10+16 MAPT mutation.

METHODS

Live imaging, electrophysiology, and redox proteomics were used in 10+16 induced pluripotent stem cell-derived neurons and a model of tau spreading in primary cultures.

RESULTS

Overproduction of mitochondrial reactive oxygen species (ROS) in 10+16 neurons alters the trafficking of specific glutamate receptor subunits via redox regulation. Increased surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors containing GluA1 and NR2B subunits leads to impaired glutamatergic signaling, calcium overload, and excitotoxicity. Mitochondrial antioxidants restore the altered response and prevent neuronal death. Importantly, extracellular 4R tau induces the same pathological response in healthy neurons, thus proposing a mechanism for disease propagation.

DISCUSSION

These results demonstrate mitochondrial ROS modulate glutamatergic signaling in FTD, and suggest a new therapeutic strategy.

Regional Neurodegeneration in vitro: The Protective Role of Neural Activity

Traumatic brain injury is a devastating public health problem, the eighth leading cause of death across the world. To improve our understanding of how injury at the cellular scale affects neural circuit function, we developed a protocol to precisely injure individual neurons within an in vitro neural network. We used high speed calcium imaging to estimate alterations in neural activity and connectivity that occur followed targeted microtrauma. Our studies show that mechanically injured neurons inactivate following microtrauma and eventually re-integrate into the network. Single neuron re-integration is dependent on its activity prior to injury and initial connections in the network: more active and integrated neurons are more resistant to microtrauma and more likely to re-integrate into the network. Micromechanical injury leads to neuronal death 6 h post-injury in a subset of both injured and uninjured neurons. Interestingly, neural activity and network participation after injury were associated with survival in linear discriminate analysis (77.3% correct prediction, Wilks' Lambda = 0.838). Based on this observation, we modulated neuronal activity to rescue neurons after microtrauma. Inhibition of neuronal activity provided much greater survivability than did activation of neurons (ANOVA, p < 0.01 with post-hoc Tukey HSD, p < 0.01). Rescue of neurons by blocking activity in the post-acute period is partially mediated by mitochondrial energetics, as we observed silencing neurons after micromechanical injury led to a significant reduction in mitochondrial calcium accumulation. Overall, the present study provides deeper insight into the propagation of injury within networks, demonstrating that together the initial activity, network structure, and post-injury activity levels contribute to the progressive changes in a neural circuit after mechanical trauma.

Excitotoxicity Revisited: Mitochondria on the Verge of a Nervous Breakdown

Excitotoxicity is likely to occur in pathological scenarios in which mitochondrial function is already compromised, shaping neuronal responses to glutamate. In fact, mitochondria sustain cell bioenergetics, tune intracellular Ca²⁺ dynamics, and regulate glutamate availability by using it as metabolic substrate. Here, we suggest the need to explore glutamate toxicity in the context of specific disease models in which it may occur, re-evaluating the impact of mitochondrial dysfunction on glutamate excitotoxicity. Our aim is to signpost new approaches, perhaps combining glutamate and pathways to rescue mitochondrial function, as therapeutic targets in neurological disorders.

Insulin Receptors and Intracellular Ca 2+ Form a Double-Negative Regulatory Feedback Loop Controlling Insulin Sensitivity

Since the discovery of insulin and insulin receptors (IR) in the brain in 1978, numerous studies have revealed a fundamental role of IR in the central nervous system and its implication in regulating synaptic plasticity, long-term potentiation and depression, neuroprotection, learning and memory, and energy balance. Central insulin resistance has been found in diverse brain disorders including Alzheimer’s disease (AD). Impaired insulin signaling in AD is evident in the activation states of IR and downstream signaling molecules. This is mediated by Aβ oligomer-evoked Ca ²⁺ influx by activating N-methyl-D-aspartate receptors (NMDARs) with Aβ oligomers directly, or indirectly through Aβ-induced release of glutamate, an endogenous NMDAR ligand. In the present opinion article, we highlight evidence that IR activity and free intracellular Ca ²⁺ concentration [Ca ²⁺] _i form a double-negative regulatory feedback loop controlling insulin sensitivity, in which mitochondria play a key role, being involved in adenosine triphosphate (ATP) synthesis and IR activation. We found recently that the glutamate-evoked rise in [Ca ²⁺] _i inhibits activation of IR and, vice versa, insulin-induced activation of IR inhibits the glutamate-evoked rise in [Ca ²⁺] _i. In theory, such a double-negative regulatory feedback loop predicts that any condition leading to an increase of [Ca ²⁺] _i may trigger central insulin resistance and explains why central insulin resistance is implicated in the pathogenesis of AD, with which glutamate excitotoxicity is a comorbid condition. This model also predicts that any intervention aiming to maintain low [Ca ²⁺] _i may be useful for treating central insulin resistance.

Singlet oxygen stimulates mitochondrial bioenergetics in brain cells

Oxygen, in form of reactive oxygen species (ROS), has been shown to participate in oxidative stress, one of the major triggers for pathology, but also is a main contributor to physiological processes. Recently, it was found that 1267 nm irradiation can produce singlet oxygen without photosensitizers. We used this phenomenon to study the effect of laser-generated singlet oxygen on one of the major oxygen-dependent processes, mitochondrial energy metabolism. We have found that laser-induced generation of ¹O₂ in neurons and astrocytes led to the increase of mitochondrial membrane potential, activation of NADH- and FADH-dependent respiration, and importantly, increased the rate of maximal respiration in isolated mitochondria. The activation of mitochondrial respiration stimulated production of ATP in these cells. Thus, we found that the singlet oxygen generated by 1267 nm laser pulse works as an activator of mitochondrial respiration and ATP production in the brain.

N-Methyl-D-Aspartate Receptor Signaling-Protein Kinases Crosstalk in Cerebral Ischemia

Although stroke is very often the cause of death worldwide, the burden of ischemic and hemorrhagic stroke varies between regions and over time regarding differences in prognosis, prevalence of risk factors, and treatment strategies. Excitotoxicity, oxidative stress, dysfunction of the blood-brain barrier, neuroinflammation, and lysosomal membrane permeabilization, sequentially lead to the progressive death of neurons. In this process, protein kinases-related checkpoints tightly regulate N-methyl-D-aspartate (NMDA) receptor signaling pathways. One of the major hallmarks of cerebral ischemia is excitotoxicity, characterized by overactivation of glutamate receptors leading to intracellular Ca²⁺ overload and ultimately neuronal death. Thus, reduced expression of postsynaptic density-95 protein and increased protein S-nitrosylation in neurons is responsible for neuronal vulnerability in cerebral ischemia. In this chapter death-associated protein kinases, cyclin-dependent kinase 5, endoplasmic reticulum stress-induced protein kinases, hyperhomocysteinemia-related NMDA receptor overactivation, ephrin-B-dependent amplification of NMDA-evoked neuronal excitotoxicity and lysosomocentric hypothesis have been discussed.Consequently, ample evidences have demonstrated that enhancing extrasynaptic NMDA receptor activity triggers cell death after stroke. In this context, considering the dual roles of NMDA receptors in both promoting neuronal survival and mediating neuronal damage, selective augmentation of NR2A-containing NMDA receptor activation in the presence of NR2B antagonist may constitute a promising therapy for stroke.

Assessment of ROS Production in the Mitochondria of Live Cells

Production of reactive oxygen species (ROS) in the mitochondria plays multiple roles in physiology, and excessive production of ROS leads to the development of various pathologies. ROS in the mitochondria are generated by various enzymes, mainly in the electron transporvt chain, and it is important to identify not only the trigger but also the source of free radical production. It is important to measure mitochondrial ROS in live, intact cells, because activation of ROS production could be initiated by changes in extramitochondrial processes which could be overseen when using isolated mitochondria. Here we describe the approaches, which allow to measure production of ROS in the matrix of mitochondria in live cells. We also demonstrate how to measure kinetic changes in lipid peroxidation in mitochondria of live cells. These methods could be used for understanding the mechanisms of pathology in a variety of disease models and also for testing neuro- or cardioprotective chemicals.

The role of prolactin in central nervous system inflammation

Prolactin has been shown to favor both the activation and suppression of the microglia and astrocytes, as well as the release of inflammatory and anti-inflammatory cytokines. Prolactin has also been associated with neuronal damage in diseases such as multiple sclerosis, epilepsy, and in experimental models of these diseases. However, studies show that prolactin has neuroprotective effects in conditions of neuronal damage and inflammation and may be used as neuroprotector factor. In this review, we first discuss general information about prolactin, then we summarize recent findings of prolactin function in inflammatory and anti-inflammatory processes and factors involved in the possible dual role of prolactin are described. Finally, we review the function of prolactin specifically in the central nervous system and how it promotes a neuroprotective effect, or that of neuronal damage, particularly in experimental autoimmune encephalomyelitis and during excitotoxicity. The overall studies indicated that prolactin may be a promising molecule for the treatment of some neurological diseases.

Neuroprotective Effect of Tricyclic Pyridine Alkaloids from Fusarium lateritium SSF2, against Glutamate-Induced Oxidative Stress and Apoptosis in the HT22 Hippocampal Neuronal Cell Line

Excessive glutamate damages neuronal cells via the accumulation of intracellular reactive oxygen species (ROS), calcium ion (Ca²⁺) influx, depolarization of mitochondrial membrane potential, and apoptosis, which may result in the development of chronic neurodegenerative diseases. In this study, we evaluated the effects of 4,6′-anhydrooxysporidinone isolated from endophytic fungus Fusarium lateritium SSF2 on glutamate-induced cytotoxicity, accumulation of intracellular ROS, increases in superoxide anion production, Ca²⁺, depolarization of mitochondrial membrane potential, and apoptotic cell death in hippocampal HT22 cells. 2′,7′-Dichlorofluorescin diacetate (H2DCFDA) staining was used to determine the intracellular reactive oxygen species concentration and dihydroethidine (DHE) staining was used to determine the superoxide radical. Expression of the nuclear factor-erythroid-2–related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) was analyzed by Western blot. Fluo-4 staining was used to determine the intracellular Ca²⁺ levels. In order to explore mitochondrial membrane potential, tetramethylrhodamine methyl ester (TMRM) staining was used. Apoptotic cell death was evaluated using Annexin-V/propidium iodide (PI) staining and TUNEL staining. Expression of the cytochrome c release and cleaved caspase-9, -3 was analyzed by Western blot. Here, we were able to isolate 4,6′-anhydrooxysporidinone from endophytic fungus, Fusarium lateritium SSF2, which was shown to protect HT22 cells from glutamate-induced cytotoxicity, accumulation of intracellular ROS, increases in superoxide anion production, Ca²⁺, and depolarization of mitochondrial membrane potential. In addition, 4,6′-anhydrooxysporidinone enhanced the expressions of Nrf2 and HO-1. It also inhibited the apoptotic cell death through the inhibition of cytochrome c release and cleaved caspase-9, -3 in glutamate-treated HT22 cells. Therefore, our results provide ample evidence of the neuroprotective properties of 4,6′-anhydrooxysporidinone.

Viscoelasticity and Volume of Cortical Neurons under Glutamate Excitotoxicity and Osmotic Challenges

Neural activity depends on the maintenance of ionic and osmotic homeostasis. Under these conditions, the cell volume must be regulated to maintain optimal neural function. A disturbance in the neuronal volume regulation often occurs in pathological conditions such as glutamate excitotoxicity. The cell volume, mechanical properties, and actin cytoskeleton structure are tightly connected to achieve the cell homeostasis. Here, we studied the effects of glutamate-induced excitotoxicity, external osmotic pressure, and inhibition of actin polymerization on the viscoelastic properties and volume of neurons. Atomic force microscopy was used to map the viscoelastic properties of neurons in time-series experiments to observe the dynamical changes and a possible recovery. The data obtained on cultured rat cortical neurons were compared with the data obtained on rat fibroblasts. The neurons were found to be more responsive to the osmotic challenges but less sensitive to the inhibition of actin polymerization than fibroblasts. The alterations of the viscoelastic properties caused by glutamate excitotoxicity were similar to those induced by the hypoosmotic stress, but, in contrast to the latter, they did not recover after the glutamate removal. These data were consistent with the dynamic volume changes estimated using ratiometric fluorescent dyes. The recovery after the glutamate-induced excitotoxicity was slow or absent because of a steady increase in intracellular calcium and sodium concentrations. The viscoelastic parameters and their changes were related to such parameters as the actin cortex stiffness, tension, and cytoplasmic viscosity.

Clinical Evidence of Antidepressant Effects of Insulin and Anti-Hyperglycemic Agents and Implications for the Pathophysiology of Depression-A Literature Review

Close connections between depression and type 2 diabetes (T2DM) have been suggested by many epidemiological and experimental studies. Disturbances in insulin sensitivity due to the disruption of various molecular pathways cause insulin resistance, which underpins many metabolic disorders, including diabetes, as well as depression. Several anti-hyperglycemic agents have demonstrated antidepressant properties in clinical trials, probably due to their action on brain targets based on the shared pathophysiology of depression and T2DM. In this article, we review reports of clinical trials examining the antidepressant effect of these medications, including insulin, metformin, glucagon like peptide-1 receptor agonists (GLP-1RA), and peroxisome proliferator-activated receptor (PPAR)-γ agonists, and briefly consider possible molecular mechanisms underlying the associations between amelioration of insulin resistance and improvement of depressive symptoms. In doing so, we intend to suggest an integrative perspective for understanding the pathophysiology of depression.

Mitochondrial Calcium Deregulation in the Mechanism of Beta-Amyloid and Tau Pathology

Aggregation and deposition of β-amyloid and/or tau protein are the key neuropathological features in neurodegenerative disorders such as Alzheimer's disease (AD) and other tauopathies including frontotemporal dementia (FTD). The interaction between oxidative stress, mitochondrial dysfunction and the impairment of calcium ions (Ca²⁺) homeostasis induced by misfolded tau and β-amyloid plays an important role in the progressive neuronal loss occurring in specific areas of the brain. In addition to the control of bioenergetics and ROS production, mitochondria are fine regulators of the cytosolic Ca²⁺ homeostasis that induce vital signalling mechanisms in excitable cells such as neurons. Impairment in the mitochondrial Ca²⁺ uptake through the mitochondrial Ca²⁺ uniporter (MCU) or release through the Na⁺/Ca²⁺ exchanger may lead to mitochondrial Ca²⁺ overload and opening of the permeability transition pore inducing neuronal death. Recent evidence suggests an important role for these mechanisms as the underlying causes for neuronal death in β-amyloid and tau pathology. The present review will focus on the mechanisms that lead to cytosolic and especially mitochondrial Ca²⁺ disturbances occurring in AD and tau-induced FTD, and propose possible therapeutic interventions for these disorders.

Inhibition of Mg2+ Extrusion Attenuates Glutamate Excitotoxicity in Cultured Rat Hippocampal Neurons

Magnesium plays important roles in the nervous system. An increase in the Mg²⁺ concentration in cerebrospinal fluid enhances neural functions, while Mg²⁺ deficiency is implicated in neuronal diseases in the central nervous system. We have previously demonstrated that high concentrations of glutamate induce excitotoxicity and elicit a transient increase in the intracellular concentration of Mg²⁺ due to the release of Mg²⁺ from mitochondria, followed by a decrease to below steady-state levels. Since Mg²⁺ deficiency is involved in neuronal diseases, this decrease presumably affects neuronal survival under excitotoxic conditions. However, the mechanism of the Mg²⁺ decrease and its effect on the excitotoxicity process have not been elucidated. In this study, we demonstrated that inhibitors of Mg²⁺ extrusion, quinidine and amiloride, attenuated glutamate excitotoxicity in cultured rat hippocampal neurons. A toxic concentration of glutamate induced both Mg²⁺ release from mitochondria and Mg²⁺ extrusion from cytosol, and both quinidine and amiloride suppressed only the extrusion. This resulted in the maintenance of a higher Mg²⁺ concentration in the cytosol than under steady-state conditions during the ten-minute exposure to glutamate. These inhibitors also attenuated the glutamate-induced depression of cellular energy metabolism. Our data indicate the importance of Mg²⁺ regulation in neuronal survival under excitotoxicity.

Insulin Receptors and Intracellular Ca 2+ Form a Double-Negative Regulatory Feedback Loop Controlling Insulin Sensitivity

Since the discovery of insulin and insulin receptors (IR) in the brain in 1978, numerous studies have revealed a fundamental role of IR in the central nervous system and its implication in regulating synaptic plasticity, long-term potentiation and depression, neuroprotection, learning and memory, and energy balance. Central insulin resistance has been found in diverse brain disorders including Alzheimer's disease (AD). Impaired insulin signaling in AD is evident in the activation states of IR and downstream signaling molecules. This is mediated by Aβ oligomer-evoked Ca 2+ influx by activating N-methyl-D-aspartate receptors (NMDARs) with Aβ oligomers directly, or indirectly through Aβ-induced release of glutamate, an endogenous NMDAR ligand. In the present opinion article, we highlight evidence that IR activity and free intracellular Ca 2+ concentration [Ca 2+] i form a double-negative regulatory feedback loop controlling insulin sensitivity, in which mitochondria play a key role, being involved in adenosine triphosphate (ATP) synthesis and IR activation. We found recently that the glutamate-evoked rise in [Ca 2+] i inhibits activation of IR and, vice versa, insulin-induced activation of IR inhibits the glutamate-evoked rise in [Ca 2+] i . In theory, such a double-negative regulatory feedback loop predicts that any condition leading to an increase of [Ca 2+] i may trigger central insulin resistance and explains why central insulin resistance is implicated in the pathogenesis of AD, with which glutamate excitotoxicity is a comorbid condition. This model also predicts that any intervention aiming to maintain low [Ca 2+] i may be useful for treating central insulin resistance.